Mozilla Corp. is considering dropping support for Windows 2000 and the earliest versions of XP when it ships the follow-up to Firefox 3.5 in 2010, online discussions show.

In a series of messages on the Mozilla.dev.planning forum, developers and Mozilla executives, including the company's chief engineer and its director of Firefox, hashed out which Microsoft operating systems it should support with the 2010 edition of its browser.

"Raise the minimum requirements on Gecko 1.9.2 (and any versions of Firefox built on 1.9.2) for Windows builds to require Windows XP Service Pack 3 or higher," said Michael Connor, one of the company's software engineers, to start the discussion.

Mozilla is currently working on Gecko 1.9.1, the engine that powers Firefox 3.5, which is still under development. The company hopes to release that browser at some point in the second quarter. Gecko 1.9.2 and the successor to Firefox 3.5 built on it -- which Mozilla has dubbed "Firefox.next" and code-named "Namoroka" -- are slated to wrap up in "early-to-mid 2010," according to the company's current plans.

Connor based his proposal on the fact that Microsoft Corp. will end all support for Windows 2000 and Windows XP Service Pack 2 on July 13, 2010, and has already ditched support for Windows XP and XP SP1. After that July 2010 date, Microsoft will only support Windows XP SP3, the free upgrade it shipped in May 2008 after some initial compatibility snafus.

"As we intend to ship the next version of Firefox in early 2010, Firefox 3.5 will continue to be supported under our current support policy (six months after the next version) until after those OS versions are no longer supported," reasoned Connor, "so users will continue to be supported by Mozilla at least as long as their OS is supported."

Some, however, balked at the idea.

"Right now, the majority of our Windows users are still on XP, but I'm not sure it's clear how many of those users have upgraded, or intend to upgrade, or in some cases are able to upgrade," said Mike Beltzner, Mozilla's director of Firefox. "And while I understand that the platform itself isn't supported by Microsoft, I do think that keeping those XP users from being able to use Firefox will end up doing more harm (to them) than good, no matter what the intent."

Others argued for even more drastic measures. "We can justify dropping [Windows 2000]/XP entirely better than setting the minimum to XP SP3 because there are many more new features in Vista that we could take advantage of," said developer Rob Arnold. "I think we should see how Windows 7 pans out. If the result is good and users migrate from XP, then we should consider dropping XP. Of course, there will always be people who cling to old systems like Win2k and XP, and they will be vocal."

Connor rebutted Arnold's argument, noting -- as did many of the others in the discussion -- that XP is hale and hearty, and may remain so for years. "I don't think completely dropping XP is feasible for [Gecko] 1.9.2 unless it ships in 2012, given that many machines, notably netbooks, are still shipping with XP Home," Connor said.

Like many of the out-in-public discussions by Mozilla -- which prides itself on the openness of its deliberations -- there was no immediate decision made by the participants, who included not only Beltzner but also Mike Shaver, Mozilla's vice president of engineering.

Currently, Firefox 3.08 supports Windows 2000, XP, Vista and Server 2003. Firefox 3.5, which will be updated to Beta 4 next week, supports the same versions.

Users of older Microsoft operating systems -- notably Windows 98 and Windows NT -- have been unable to upgrade from Firefox 2.0 to the Version 3.x line, a point that has irked many.